Self oscillating light controlled circuit



` Sept. 22, 1959 E. G. MATKlNs ET AL 2,905,858

SELF oscILLATING LIGHT coNIRoLLED CIRCUIT Filed Sept. 2, 1954 INVENTORS ATTDRNEY SELF OSCILLATZNG LIGHT CONTROLLED CIRCUIT Eugene G. Matkins, Reelsville, and Charles W. Miller,

Anderson, Ind., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application September 2, 1954, Serial No. 453,763 2 Claims. (Cl. 317-130) This invention relates to a light sensitive control system and more particularly to a light sensitive control system which may be used to control the energization of the bright and dim filaments of automobile headlamps.

Current automatic light sensitive control systems for dimming automobile headlamps utilize relatively high voltages. In order to provide such voltages it is necessary to incorporate a power pack or voltage supply unit which supplies the necessary higher voltages from a conventional storage battery source.

It is an object in making our invention to provide a light sensitive control system, the components of which do not require any higher voltages than those supplied by the conventional storage battery, and therefore a separate power supply section may be omitted.

,lt is a further object in making our invention to provide a light sensitive control system for automotive vehicles which will operate entirely from storage battery voltage.

It is a further object in making this invention to provide a light sensitive control system which is non-oscillatory in the absence of light, but which becomes oscillatory at a certain predetermined light intensity to produce a control voltage for switching headlamp beams.

With these and other objects in view which will become apparent as the specification proceeds, our invention will be best understood by reference to the following specification and claims and the illustrations in the accompanying drawing, in which:

The figure is a circuit diagram of a control system embodying our invention.

As indicated above, the general character of the present automatic control system is that it is an oscillatory system which in the absence of light is non-oscillatory, but which breaks into oscillation and continues to oscillate and produce an oscillating voltage when light of a predetermined intensity continues to fall on the control photocell. The output of the oscillator controls a power amplifier, which, through a sensitive relay, controls a power relay to actually switch the beam energization.

Referring now more particularly to the drawing, line 2 is directly connected to any suitable source of electrical power, such for example as the storage battery of a conventional automobile. Line 2 is directly connected through line 4 to one terminal of the operating coil 6 of a relay 8, the opposite terminal of said coil 6 being connected directly to plate 10 of the power amplifying tube 12. Relay 8 also includes a pivotally movable armature 14, which is electrically connected to line 4, and which oscillates between two stationary contacts 16 and 18, contact 18 being provided merely as a mechanical stop to prevent further movement of the armature 14 when it is attracted by the operating coil 6 and moved away from engagement with the other stationary contact 16. When the operating coil 6 is not energized, a spring bias holds armature 14 against contact 16.

Contact 16 is connected through line 20 with one terminal of the operating coil 22 of the power relay 24, the opposite terminal of which is grounded. Power relay 24 also includes a pivotally movable armature 26 which is spring biased downwardly as indicated in the drawing into United States Patent O Mice engagement with a stationary contact 28 connected di rectly to the upper beam filaments indicated as HI. When the relay coil 22 is energized, the armature 26 is moved upwardly against the spring bias into engagement with stationary contact 30 connected directly to the lower beam filaments indicated as LO. Armature 26 is directly connected through line 32 to the source of power such as the battery. Thus when relay 24 is deenergized, a circuit is completed to the upper beam or high filaments and when energized the circuit to the upper beam filaments is broken and one completed to the lower beam filaments.

Line 2 is directly connected to one side of a ballast tube 34, the opposite side of which is connected directly to a second regulated power supply line 36. The oscillator in this instance is of the multivibrator type and consists of two tubes 38 and 40. Plate 42 of tube 38 is directly connected through a limiting resistor 44 with the regulated power supply line 36. The suppressor grid 46 of tube 38 is connected to ground through biasing resistor 48, and through a coupling condenser 50 with the plate 52 of the tube 40. The screen grid 54 of tube 38 is con'- nected directly to the regulated power supply line 36. Control grid 56 of tube 38 is connected to the cathode 58 of the photoelectric cell 60. This connection is enclosed by grounded shield to prevent control grid S6 from being aiected by external voltages. The anode 62 of this cell is connected directly to regulated power supply line 36. The cathode 64 of tube 38 is connected directly to ground.

Plate 42 of tube 38 is also connected through a coupling condenser 66 to the control grid 68 of tube 40. A variable resistor 70 is connected between grid 68 and ground to vary the bias on said grid. Screen grid 72 of tube 40 is connected directly to the regulated supply line 36, as is screen grid 54 in the rst tube. The suppressor grid 74 is connected directly to ground and to the lower terminal of a resistor 76, the opposite terminal of which is connected to power supply line 36. A variable tap 78, movable over resistor 76, is connected to one end of a limiting resistor 80, the opposite end of which is di.- rectly connected to plate 52 to thus vary the plate potential of this tube. The laments 82 and 84 of the two tubes 38 and 40 are supplied with power through resistor 86 connected between the regulated power supply line and the iilaments by an obvious circuit. A resistor 88 is connected between the regulated line 36 and ground.

The output of the oscillator formed by the tubes 38 and 40 is applied to the control grid 94 through coupling condenser 92 from plate 42. Screen grid 96 of the power amplifier tube 12 is directly connected to the regulated power supply line 36. The suppressor grid 98 is connected directly to the cathode 100 which is grounded. The iilament 102 of the tube 12 is supplied with power through a resistor 104 connected directly to line 36. A biasing resistor 106 is connected between control grid 94 and ground.

The values of the components of the present system are so selected that when no light falls on the photocell 69, the tube 38 is not conducting. The second tube of the oscillator section 40 is conducting in the no-light condition, and the power amplifier tube is likewise conducting providing sufficient current flow through operating coil 6 to cause it to overcome the spring bias and attract armature 14. Thus no circuit is completed to the operating coil 22 of power relay 24, and therefore the spring bias maintains the armature 26 in its lower position, completing an obvious circuit for the high beams.

As the amount of incident light falling on the photocell 60 increases, the bias on the control grid 56 becomes more and more positive until at a certain point tube 38 conducts, When this occurs the potential on the plate aooea 42 thereof decreases. Since, through conventional multivibrator connections, tube 38 is connected across condenser 66 and resistor 70, condenser 66 discharges to lower the potential on grid 68 of tube 40 to cut ofi conductance through this tube, which raises the plate voltage of tube 40, changing condenser 50 to a higher value and increasing the potential of suppressor grid 46 to assist in maintaining ow through tube 38. When the condenser 66 is discharged, grid 68 becomes more positive and tube 4t) conducts to drive tube 38 into a noneonductive condition and the system continues to oscillate in a known m-anncr as long as there is sufficient light on the photocell to keep conductive periods in said tube 38. VThis oscillatory action causes a series of positive pulses to appear in the plate circuit of tube 38 which are applied to the control grid 94 of the power amplifier tube 12 through condenser 92. While the pulses on the control grid 94 are positive, they produce a negative bias Vthrough the rectifying action of the cathode and grid 10ft-94. Driving of the grid 94 negative tends to cut off conduction through the power amplifier stage 12 and operating coil 6 releases its armature 14, which moves into engagement with stationary contact i6, completing an energizing circuit for operating coil 22 of power relay 24. This moves its armature 26 away from the lower stationary contact 28 and into engagement with the upper contact 30 to deenergize the upper beam filaments and energize the lower beam filaments. As long as the amount of light falling on the photocell 68 is maintained above a predetermined level and the oscillator provides the series of pulses, the switching system will remain on low beam energization. However, as soon as the light is removed, the oscillator will stop and the power amplifier tube will resume conduction to switch oft the low beam filaments and energize the high beam ones.

The adjustable means for determining the sensitivity at which the system will cause a switching from high to low filaments is through movement of the adjustable tap 78 on resistance 76. This will vary the potential applied to the plate 52 of the tube 40, and therefore contrcls the starting condition of oscillation. The adjustment of the system to determine the sensitivity at which it will drop out of oscillation is obtained through adjustment of the variable resistor 70, which determines the bias on the control grid 68 of the second tube 40. This controls the point at which the reduction of light permits the oscillator to stop oscillating.

We claim:

1. A control systemA for automatically switching vehicle headlamps from high beam to low beam at one value f incident light intensity and from low beam to high beam at a second value of incident light intensity, said system comprising a multivibrator having first and second electron tubes each having a cathode and a plate and having first and second grids for controlling the current flow therebetween, a voltage source having one terminal connected to ground, said tubes being connected in crosscoupled fashion wherein the plate of the first tube is connected through a fixed plate load resistor to the other terminal of the voltage source and the plate of the second tube is connected through an adjustable plate load resistor to the other terminal of the source and the cathodes are connected to ground, the first grid of the first tube being connected to the plate of the second tube by a condenser and to ground by a fixed resistor, the first grid of the second tube being connected to the plate of the first tube by a condenser and to ground by a variable resistor, a photocell operatively connected with the second grid of the first tube for developing a voltage thereon which increases with incident light intensity tending to cause conduction of the first tube, the second grid vof the second tube being connected to said other terminal resistor being adjusted to permit the second tube to become non-conductive and the first tube to become conductive upon the occurrence of said one value of incident light intensity whereby the two tubes conduct alternately to generate sustained oscillations in the multivibrator, an amplifier having an input circuit coupled with said multivibrator and an output circuit including a relay, whereby the amplifier and relay are maintained in one condition of energization when the multivibrator gen` crates sustained oscillations, said variable resistor being adjusted to terminate. oscillations in the multivibrator to change the energization of said amplifier and relay when the incident light intensity diminishes to the second value.

2. A control system for automatically switching vehicle headlamps from high beam to low beam at one value of incident light intensity and from low beam to high beam at a second Ivalue of incident light intensity, said system comprising a multivibrator having rst and second electron tubes each having a cathode and a plate and having first and second grids for controlling the current flow therebetween, a voltage source having one terminal connected to ground, said tubes being connected in cross-coupled fashion wherein the plate of the first tube is connected through a fixed plate load resistor to the other terminal of the voltage source and the plate of the second tube is connected through an adjustable plate load resistor to the other terminal of the source and the cathodes are connected to ground, the first grid of the first tube being connected to the plate of the second tube by a condenser and to ground by a fixed resistor, the rst grid of the second tube beinfy connected to the plate of the first tube by a condenser and to ground by a variable resistor, a photocell connected between said other terminal of the voltage source and the second grid of the first tube for developing a. voltage thereon which increases with incident light intensity tending to cause conduction of the first tube, the second grid of the second tube being connected to said other terminal of the voltage source whereby the second tube is conductive and the first tube. is non-conductive in the absence of light on the photocell, said variable plate load resistor being adjusted to permit the second tube to become non-conductive and the first tube to become conductive upon the occurrence of said one value of incident light intensity whereby the two tubes conduct alternately to generate sustained oscillations in the multivibrator, an amplier tube with plate, cathode andgrid, a relay including an energizing coil connected between the amplifier tube plate and the said other terminal of the voltage source, the amplifier tube having its cathode connected to ground and its grid coupled to the plate of the first tube through a condenser and to ground through a resistor whereby the amplifier tube is maintained non-conductive by the pulsating voltage on the plate of the first tube and the relay is deenergized when the multivibrator generates sustained oscillations, said variable resistor being adjusted to. permit oscillations in the multivibrator to continue until the incident light intensity diminishes to the second value.

References Cited in the file of this patent UNITED STATES PATENTS 1,749,295 Messtorl Mar. 4, 1930 2,228,163 Cohen Jan. 7, 1941 2,248,975 Fandell July 15, 1941 2,280,978 Roberts Apr. 28, 1942 2,281,934l Geiger May 5, 1942 2,549,875r Williams et al Apr. 24, 1951 2,590,826 Schenck Mar. 25, 1952 2,695,962 Nibbe Nov. 30, 1954 2,730,629 Atkins Jan. 10, 1956 2,741,725 Thomas Apr. 10, 1956 FOREIGN PATENTS 456,840- Great Britain Nov. 12, 1936 

